LiOtBu-Promoted Intramolecular 1,3-Dipolar Cycloaddition of the 2′-Alkynyl-biaryl-2-aldehyde N-Tosylhydrazones Approach to 3-Substituted 1H-Dibenzo[e,g]indazoles

A two-step, one-pot synthesis of 3-substituted 1H-dibenzo[e,g]indazoles in good to high yields via a LiOtBu-promoted intramolecular 1,3-dipolar cyclization of 2′-alkynyl-biaryl-2-aldehydeN-tosylhydrazones was developed. TheN-Ts-hydrazones used were prepared in situ via the reactions of 2′-alkynyl-biaryl-2-aldehydes and TsNHNH2(p-methylbenzenesulfonohydrazide). Two types of signals related to the hydrogen bonds, forming in several products, were observed in the1H NMR spectra recorded in DMSO-d6, assigned to N-H bonds in their dimeric species of product and tautomer.Keywords:N-tosylhydrazones;1H-dibenzo[e,g]indazoles;intramolecular cycloaddition;lithiumtert-butoxide;hydrogen bonds